1. Field of the Invention
The present invention relates to an electrostatic copying apparatus, and more particularly to a copying apparatus possessing a first exposure mode for fixing the original and reading the original image by scanning an exposure means for reading the original image optically, and a second exposure mode for fixing the exposure means and reading the original image by conveying the original to be read by, for example, a recirculating automatic document feeder (RADF).
2. Description of the Prior Art
In an electrostatic copying apparatus, when copying a plurality of documents, the so-called RADF may be installed in order to save the labor of the operator for putting the documents one by one on the original platen. This RADF sequentially conveys the plurality of documents in synchronism with the copying action of the electrostatic copying apparatus main body, and realizes the function of copying duplex documents having the original images to be copied on both sides of copying papers in cooperating with the main body.
The electrostatic copying apparatus having the RADF possesses at least two exposure action modes. That is, in a first exposure mode, the document is placed on the original platen which is a first reading region so that the original image to be copied may confront it, and an exposure means containing an exposure lamp such as a halogen lamp and a reflector mirror disposed at the lower side (the inner side of the electrostatic copying apparatus main body) of the original platen runs at a constant speed, and the original image is read by optical scanning. On the other hand, in a second exposure mode, the documents are conveyed one by one by the RADF, for instance, as being wound around a conveying means of right cylindrical shape, and the exposure means is stopped in a predetermined second reading region near the conveying means, and the original image of the conveyed document is optically scanned and read. The first reading region and the second reading region are disposed at a specific interval on the upper part of the main body.
The light from the exposure lamp of the exposure means is led into the original image to be read of the document, and is selectively absorbed corresponding to the original image. The reflected light from the original image is led into a surface of a photosensitive drum of right cylindrical shape by way of plural reflector mirrors and a zoom lens or the like. In relation to this photosensitive drum, a main corona discharger, a developing device, a transfer corona discharger, and a cleaning device or the like are disposed. The surface of the photosensitive drum is uniformly charged by the main corona discharger, and is selectively destaticized by the light from the exposure means afterwards, and an electrostatic image corresponding to the original image of the document which has been read is formed. This electrostatic image is made sensible into a toner image by the developing device. The toner image is transferred on the copying paper by the function of the transfer corona discharger, and is heated and fixed on the copying paper by a fixing device installed at the downstream side in the conveying direction of the copying paper from the transfer corona discharger. After transfer of the toner image, the toner remaining on the surface of the photosensitive drum is removed by the cleaning device.
In the first exposure mode, the running of the exposure means and the action of the copying process near the photosensitive drum are controlled so as to have a synchronous relationship, and in the second exposure mode, these are controlled so that the conveying action of documents in the RADF and the action of the copying process near the photosensitive drum may have a synchronous relationship. In this way, a favorable copy image may be formed on the copying paper in either mode.
In such electrostatic copying apparatus, the two exposure modes are selected by the operator. Usually, while the copying apparatus is waiting for a selection input of the exposure mode, the exposure means is waiting at the stopping position of the exposure means in the second exposure mode. Afterwards, when the second exposure mode is selected, since the exposure means is already set at the specified stopping position, the copying action in the second exposure mode is started.
When the first exposure mode is selected, on the other hand, the exposure means waiting at the stopping position in the second exposure mode starts to move to the first reading region for the copying action in the first exposure mode. After start of running, the quantity of light of the exposure lamp is raised to the specified level, and the speed is raised to the specified scanning speed just before reaching the first reading region, thereby getting into the first reading region. Later, after the exposure means passes through the first reading region and optically scans the original image of the document to be read, the running direction of the exposure means is inverted, and returns to the stopping position in the second exposure mode. That is, in the first exposure mode, the scanning start position of the exposure means to the first reading region and the scanning end position are both the stopping position of the exposure means in the second exposure mode.
Conventionally, for the document to be read, which is put in the first reading region, the moving range of the exposure means for copying action plural times is not different from the moving range of the exposure means for a single copying action. Therefore, when performing copying action plural times, every time, the running of the exposure means, which starts for scanning from the stopping position in the second exposure mode and returns to the stopping position, is repeated.
In the case of copying plural times, however, when it is designed so that subsequent optical scanning cannot be started unless the exposure means after the optical scanning has returned to the scanning end position which is same as the scanning start position again, it requires a very long time to start second optical scanning in succession after end of first optical scanning, and the copying operation speed cannot be decreased. In particular, when the interval between the scanning start position (scanning end position) and the first reading region for placing the document is relatively wide, a longer time is required.